Implantable prosthetic devices such as artificial hips, knees, ankles, elbows, and shoulders, as well as spinal cord implants, must provide for movement or articulation of multiple parts or members. Generally, one member moves relative to a second member that is fixed and formed from wear-resistant plastic, for example, ultra-high molecular weight polyethylene.
The repeated movement of the respective members of the prosthetic implant will wear the softer plastic causing deterioration. It is generally an object of these prosthetic devices to minimize this wear to the extent possible. This involves a trade-off of relative characteristics. Ceramic surfaces provide reduced wear, but are more brittle. Metals possess the requisite strength but cause additional wear.
Certain alloys provide less wear; for example cobalt-chromium-molybdenum alloys provide very low wear. However, there is concern about metal ion release from certain of these alloys with the possibility of causing an allergic reaction. Titanium or titanium alloy load bearing members are extremely strong, but can cause more wear than, for example, a ceramic or cobalt-chromium-molybdenum alloy member.